It is well known to use ellipsometry to determine thickness and optical constants of thin film materials. It is also known that ellipsometry provides a correlated product of thickness and refractive index. One known approach to breaking the correlation is to investigate two samples which have different thicknesses of the same material thereupon, and simultaneously perform regression of mathematical models for the two samples onto ellipsometric data obtained from each. The presently disclosed invention proposes a different approach to breaking the identified correlation involving gaining insight to the “effective thickness”, (ie. thickness per se. as modified by surface coverage, roughness and/or porosity etc.) of a material caused to accumulate on the surface of an oscillating means, and using said insight in evaluating the product of the “effective” thickness and optical constants via ellipsometric techniques. That is, if an effective thickness of a material is determined by other techniques, and the product of said effective thickness and refractive index of a material is determined by ellipsometric techniques, then the refractive index can be determined by a simple division.
A Search for relevant reference material has provided Patents:
U.S. Pat. No. 6,125,687 to McClelland et al. which describe a system for determining outgassing comprising a microbalance.
U.S. Pat. No. 4,561,286 to Sekler et al. which disclosed a piezoelectric detector.
U.S. Pat. No. 4,735,081 to Luoma et al. which discloses a detector for detecting vapors is gaseous fluids comprising a crystal oscillator.
Articles which were identified are:
“Surace Specific Kinetics of Lipid Vesicle Adsorbtion Measured With a Quartz Microbalance”, Keller et al., Biophysical Journal, Vol. 75, (1998). This article discusses simultaneous frequency and dissipation measurements performed on QCM provide an efficient approach to measuring the kinetics of lipid vesicle adsorbtion and characterizing adsorbed layers.
“Simultaneous Monitoring of Protein Adsorbtion at the Solid-Liquid Interface From Sessile Solution Droplets by Ellipsometry and Axisymmetric Drop Shape Analysis by Profile”, Noordmans et al., Colloids and Surfaces B: Biointerfaces 15, (1999). This article discusses combination of aqueous phase atomic force microscopy, ellipsometry and axisymmetric drop shape analysis by profile (ADSA-P).
“Characterization of PNA and DNA Immobilization and Subsequent Hybridization with DNA Using Acoustic Shear-Wave Attenuation Measurements”, Hook et al., Langmuir 17, (2001). This article discusses combined use of a quartz microbalance and dissipation monitoring can characterize the bound state of single-stranded peptide nucleic acid (PNA) and deoxyribose nucleic acid (DNA).
“Relaxation Dynamics in Ultrathin Polymer Films”, Forrest et al., Physical Review E, Vol. 58, No. 2, (1998). This paper describes combined application of Photon Correlation Spectroscopy and Quartz Balance Microbalance.
“Structural Changes in Hemoglobin During Adsorbtion to Solid Surfaces: Effects of Ph, Ionic Strentth, and Ligand Binding”, Hook et al., Proc. Natl. Acad. Sci., Vol. 95, (1998). This article describes application of a Quartz Microbalance technique to follow Hb adsorption onto a surface. The Quartz Crystal Microbalance (QCM) system is described in this article as comprising a disk shaped, AT-cut Piezoelectric Quartz Crystal with metal electrodes deposited on two faces. In use the crystal is excited to oscillation in the thickness shear mode at its fundamental resonance frequency (f), by applying a RF Voltage across the electrodes near the resonant frequency. A small mass (ΔM) added to the electrode induces a decrease in the resonant frequency (Δf) which is proportional to the (Δm), providing that the mass is evenly distributed, does not slip on the electrode and is sufficiently rigid and/or thin to have negligible internal friction. An equation is given which provides a quantitative descriptions:ΔM=(CΔf)/nwhere C (=17.7 ng cm−2 Hz−1 at f=5 MHz), is the mass-sensitivity constant and n(=1, 3, . . . ) is the overtone number.Also disclosed are materials from “Q-SENSE” which disclose Quartz Micro-Balance systems:                “Q-SENSE D300”;        “QCM-D Applications, Biosurfaces in Depth”;        “Investigating the Sticking Power of Blue Mussels”.        
Finally, the methodology of ellipsometry is described in many references such as U.S. Pat. No. 5,373,359 to Woollam et al., U.S. Pat. No. 5,872,630 to Johs et al., U.S. Pat. No. 5,963,327 to He et al., U.S. Pat. No. 6,353,477 to Johs et al., U.S. Pat. No. 6,034,777 to Johs et al., U.S. Pat. No. 6,456,376 to Liphardt et al., U.S. Pat. No. 5,706,212 to Thompson et al. and U.S. Pat. No. 5,666,201 to Johs et al. An article by Johs titled “Regression Claibration Method for Rotating Element Ellipsometer”, Thin Film Solids 234 (1993); an Article by Collins titled “Automatic Rotating Element Ellipsometers: Calibration, Operation and Real-time Applications”, Rev. Sci. Instrum. 61 (8) (1990), and a book by Azzam & Bashara titled “Ellipsometry and Polarized Light”, North-Holland (1977) is also disclosed.
Briefly, ellipsometry causes a polarized beam of electromagentic radiation to interact with a sample surface and then enter a detector. Changes in polarization state in the beam caused by the sample are represented by ellipsometric PSI and DELTA which are identified by:ρ=rp/rs=Tan(Ψ) exp(iΔ)where rp and rs are orthogonal components of the beam perpendicular and parallel to, respectively, the sample surface.A mathematical model of the Sample is proposed and a regression procedure applied to convert the PSI and DELTA values to Sample representing values such as correlated thickness and optical constant values corresponding to various wavelengths and angles of incidence of the beam to the sample surface.The forgoing references are incorporated by reference herein.
Even in view of known Prior Art, need remains for a system and method to combine Spectroscopic Ellipsometry and Quartz Microbalance techniques to the end of providing uncorrelated determination of both thickness and optical constants of deposited materials.